The present invention relates generally to signaling protocols used in telecommunications networks, and more particularly, to an interface between a gateway to an SS7 telecommunications network, such as the Public Land Mobile Network (PLMN), and an Internet Protocol (IP) telecommunications network, such as a private wireless office network.
In a cellular communication network, a geographical area or calling area is divided into smaller coverage zones called cells. Each cell is served by a base station that communicates with mobile phones within that particular cell. The base stations are linked to a Mobile Services Switching Center (MSC) that in turn is connected to other MSCs as well as the Public Switched Telephone Network (PSTN).
Many cellular networks are interconnected to form the Public Land Mobile Network (PLMN). The area serviced by a particular cellular network in the PLMN is referred to as a calling area. The interconnection of many different cellular networks allows mobile subscribers to maintain service while xe2x80x9croamingxe2x80x9d outside the service area of their home provider. The MSC is responsible for connecting calls that originate or terminate in the PLMN.
To carry out the business of requesting services, connecting calls, and sharing information that is needed to provide telecommunications services to mobile subscribers, the MSCs in the cellular network must exchange information with one another. In modern cellular communication systems, a signaling network provides the communication link between MSCs in a cellular network. This signaling network is used by the MSCs to exchange information needed to carry out the business of connecting and disconnecting voice and data circuits and providing other services. For example, the signaling network is used by the MSC to request connection to a voice or data circuit controlled by another MSC. The signaling network is also used to provide services, such as roaming, and to invoke advanced features of the network, such as automatic callback. The signaling network is separate from the voice network and is used solely for the purpose of communicating messages between nodes in the network necessary to the business of connecting calls and maintaining the network. An example of a signaling network is the SS7 network. SS7 is an international standard network signaling protocol that allows common channel signaling between entities within a network.
In order to permit the orderly exchange of information, nodes of a network must agree to a specific communications protocol. The protocol must be strictly followed by each node participating in a communication session to properly deliver data between the nodes. In the PLMN, that protocol is the SS7 protocol. SS7 is a message-based, packet switching protocol that provides connectionless services. In the SS7 network, an entity requests services from another network entity by sending a message without establishing a physical connection to the destination node. These messages travel from node to node over the network from the originating node to the destination node in a envelope called a packet. An important feature of the SS7 protocol is its layered architecture. The functions of the protocol are divided into layers. Each message transmitted will contain many layers of information. When a message is sent, it is passed down through the various layers of the protocol stack at the originating node, over the physical medium to the destination node, and back up the protocol stack at the destination node. As the message travels down the protocol stack, each layer adds information in a header to the message that is needed by the protocols at that layer. As the message travels up the protocol stack at the destination node, the header information is stripped off at each layer. Thus, each layer acts as an envelope to transport messages generated by the layer above.
Two important protocols used in cellular communications networks are the Mobile Application Protocol (MAP) and the Transaction Capabilities Control Protocol (TCAP). The MAP protocol is an extension of the SS7 protocol adapted for use in cellular networks. One of the main functions of the MAP protocol is to provide seamless roaming between cellular networks so that cellular subscribers do not have to pre-arrange for roaming services. The MAP protocol defines the messages and transactions for exchanging subscriber information between nodes that is needed to implement seamless roaming services. As a result, a cellular subscriber can travel from one calling area to another without pre-arrangement of loss of service. The MAP protocol makes roaming transparent to the user.
The MAP protocol relies on the TCAP protocol to retrieve subscriber information from network databases. TCAP is an SS7 protocol that is used to provide access to network databases. In the intelligent network, TCAP protocol is also used by one node to invoke features, such as automatic callback, at another node.
In recent years, there has been much interest in building private wireless office telephone systems (WOTS) by corporations or other large entities. Private wireless office telephone systems employ many concepts and features used by cellular networks and may be thought of as a scaled down cellular network. A plurality of micro base stations are positioned throughout the office to provide radio coverage within the office for mobile telephones. These base stations are connected to a switching center that is similar to the MSC in a cellular network. The switching center provides connection to the PSTN to allow users in the private wireless office system to communicate with the PSTN.
The main advantage of a WOTS is that it allows customers to use wireless telephones in an office or other localized area rather than a desk phone with a fixed connection to the telephone system. This allows customers to have mobility within the office yet remain accessible by phone.
In order to fully realize the potential of the wireless office telephone system, it is desirable to also interface the WOTS with the PLMN. Interfacing with the PLMN allows users of the WOTS to use a single mobile phone in both networks. That is, a user of the private wireless office telephone system could use the same mobile phone when xe2x80x9croamingxe2x80x9d in the PLMN. To make roaming in the PLMN possible, the private wireless office telephone system must be able to communicate with the PLMN. Thus, the private wireless office telephone system must implement the application layer protocols already in use in the PLMN. Those protocols include the Mobile Application Protocol (MAP) and the Transaction Application Control Protocol (TCAP).
In an SS7 network, the TCAP protocol relies on the services of a transport protocol called the Signaling Connection Control Part (SCCP) to deliver messages over the network. The SCCP layer provides the routing information needed to deliver messages over the SS7 network. Information contained in the SCCP layer includes the origination and destination addresses that are used to route messages through the network or series of networks.
Existing implementations of the private wireless office telephone systems also use the SCCP protocols for transporting messages over the private wireless office network. This means that the nodes in the wireless office telephone system must be assigned SS7 addresses and participate in SS7 message management at the SCCP layer. The SCCP layer adds additional signaling overhead that is not needed in wireless office telephone systems that use the TCP/IP protocols for addressing and routing of messages. In TCP/IP networks, addressing is managed by the IP layer. The TCP layer is also capable of providing transport services similar to SCCP. Eliminating support for the SCCP protocols would greatly simplify the private wireless office system and eliminate redundancy in the existing protocols. Therefore, there is a need for a protocol and interface that allows TCAP and MAP messages to be transported over an existing TCP/IP network without the need to implement the SCCP or lower level SS7 protocols in the private wireless office network.
The present invention relates to an interface between an SS7 gateway and an IP network. The interface allows messages addressed using the IP protocol to be transmitted via said interface to an SS7 gateway and then formatted for transmission over said SS7 network. The invention is particularly useful for connecting a private wireless office system to an SS7 network to allow roaming between the private wireless office telephone system and the PLMN. The invention allows application layer data, such as MAP and TCAP messages, to be transported unchanged through the interface. The invention also provides a protocol for transporting MAP and TCAP messages that eliminates the need for SS7 protocols, and in particular, eliminates the need to implement the Signaling Connection Control Part (SCCP).
According to the present invention, mobile application messages (MAM) are transported through the interface to the SS7 gateway using a protocol called the Private Wireless Office Protocol (PWOP). MAM messages are encapsulated in a PWOP layer having address information elements identifying the called party and the calling party. In messages originating in the IP network, the calling party address is populated with the IP address of the originating host in the IP network. The calling party address is translated by the interface into a SS7 address. The message is also reformatted by the interface to render it suitable for transmission over the SS7 network. Messages originating from a node in the SS7 network are received by the SS7 gateway and transmitted over the interface to a host in the IP network. Since the hosts in the IP network are not addressed using a SS7 address, the interface must translate the called party address from a SS7 address to an IP address identifying the destination host in the IP network. To perform this conversion, the interface uses a database that stores the IP addresses for hosts in the IP network along with a corresponding SS7 address. The interface replaces the SS7 calling party address with the corresponding IP address retrieved from the database and reformats the message for transmission over the IP network.
The PWOP protocol also defines procedures for establishing a communication session between the SS7 gateway and a host in the IP network. Those procedures include the session management procedures and link supervision procedures. The session management procedures are used to open and close communication sessions, and to configure the IP host for communication with the SS7 gateway. The link supervision procedures are used to monitor the link between the SS7 gateway and the IP network and to reestablish the link in the event that a problem arises.
The present invention provides a means for using IP to transport mobile application messages, such as MAP and TCAP messages, without intervening SS7 protocol layers. One of the benefits of the invention is that it provides a relatively simple yet robust transport protocol that eliminates the need for hosts in the IP network to have any knowledge of SS7 protocols or to participate in SS7 message management. The present invention also allows current MAP/TCAP protocols to be used within the IP network.